1. Field of the Invention
The present invention relates to a method and apparatus for direct energy conversion. More specifically, the invention relates to a method and apparatus for direct energy conversion for converting the optical energy of an external photon beam into electricity by employing the unique properties of Type II high temperature superconductors.
2. Related Art
The following definitions are used herein:
Atomic Force In the normal state of matter, electrons are kept apart by mutual repulsion based on their electrostatic and magnetic properties. In the case of Type II superconductors, for example, YBCO, electrons that normally repel one another experience an overwhelming attraction to link up and form Cooper pairs when the material drops below its critical temperature, Tc. When these electrons form Cooper pairs, they take on the character of bosons, meaning that all the electrons have the same spin and energy level. Only bosons can condense and occupy a ground state that has a lower total energy than that of the normal ground state. This behavior suggests that Cooper pairs are coupling over hundreds of nanometers, three orders of magnitude larger than the crystal lattice spacing. The effective net attraction between the normally repulsive electrons produces binding energy on the order of milli-electron volts, enough to keep them paired at low temperatures. Electrons in the Cooper pair state can be considered compressed because they are closer to each other than in the normal (non-superconducting) state. In many ways, Cooper pair electrons are much like a mechanical spring under compression. The atomic force is defined as the compressive force provided by millions of Cooper pairs in this ground state. The available potential energy increases when electrons close their interaction distance. This potential energy is released when the Cooper pair electrons absorb the energy of photons and are forced to revert from their lower total energy ground state to the higher total energy normal ground state. When this happens, the potential energy is released in a fraction of a second, producing spontaneous symmetry breaking (also known as Photon Cooper Pair Breaking). The cycle is repeated once the electron ejects a photon of a lower energy level and transitions back to the lower total energy ground state.
B: The magnetic field in which a superconductor is placed
Cooper pair: Two electrons that are bound together in accordance with the conventional Bardeen-Cooper-Schrieffer theory of superconductivity, despite the fact that they both have a negative charge and normally repel each other. Below the superconducting transition temperature Tc, paired electrons form a condensate (a macroscopically occupied single quantum state), which flows without resistance.
Flux lines: A magnet's lines of force.
Fluxoid (also known as flux line, fluxon, vortex): One of the microscopic filaments of magnetic flux that penetrates a Type II superconductor in the mixed state, consisting of a normal core in which the magnetic field is large, surrounded by a superconducting region in which flows a vortex of persistent supercurrent which maintains the field in the core.
Conventional Flux-Pinning: The phenomenon where a magnetic flux become trapped or “pinned” inside a current-carrying Type II superconducting material in spite of the Lorentz force acting to expel it from inside the Type II superconducting material. Flux pinning is only possible when there are defects in the crystalline structure of the superconductor (usually resulting from grain boundaries or impurities).
Hc2: The “upper critical field” or maximum magnetic field that a superconductor can endure before it is “quenched” and returns to a non-superconducting state. Usually a higher Tc also brings a higher Hc2.
Meissner Effect: The exhibiting of diamagnetic properties to the total exclusion of all magnetic fields. The Meissner Effect is a classic hallmark of superconductivity.
Quantum efficiency: In an optical source or detector, the ratio of the number of output quanta to the number of input quanta.
Quench: The phenomenon where superconductivity in a material is suppressed; usually by exceeding the maximum current the material can conduct (Jc) or the maximum magnetic field it can withstand (Hc).
Tc: The critical transition temperature below, which a material begins to superconduct.
Thin Film (Deposition): A process for fabricating ceramic superconductors to more precisely control the growth of the crystalline structure to eliminate grain boundaries and achieve a desired Tc. Two types of thin film deposition are Pulsed-Laser Deposition (PLD) and Pulsed-Electron Deposition (PED) of the material.
Vortices (plural of vortex): Swirling tubes of electrical current induced by an external magnetic field into the surface of a superconducting material that represent a topological singularity in the wave function. These are particularly evident in Type II superconductors during “mixed-state” behavior when the surface is just partially superconducting. Superconductivity is completely suppressed within these volcano-shaped structures. The movement of vortices can produce a resistance and, as such, is undesirable. While superconductivity is a “macroscopic” phenomenon, vortices are a “mesoscopic” phenomenon.
YBCO: An acronym for a well-known ceramic superconductor composed of Yttrium, Barium, Copper and Oxygen. YBCO was the first truly “high temperature” ceramic superconductor discovered, having a transition temperature well above the boiling point of liquid nitrogen (a commonly available coolant). Its actual molecular formula is YBa2Cu3O7, making it a “1-2-3” superconductor. YBCO compounds exhibit d-wave electron pairing.
Superconductivity, discovered in 1911 by Heike Kamerlingh Onnes, is a phenomenon occurring in many electrical conductors at extremely low temperatures (on the order of −200° Celsius). In this phenomenon, the electrons responsible for conduction undergo a collective transition into an ordered state, an electronic fluid consisting of Cooper pairs. Attractive force between electrons from the exchange of phonons causes the pairing of electrons in Cooper pairs. As a result of its ordered state, the Cooper pair fluid has many unique and remarkable properties, including the vanishing of resistance to the flow of electric current, the appearance of a large diamagnetism and other unusual magnetic effects, substantial alteration of many thermal properties, and the occurrence of quantum effects otherwise observable only at the atomic and subatomic level.
One of the unusual magnetic effects exhibited by superconductors is the Meissner (or Meissner-Ochsenfeld) Effect. Meissner and Ochsenfeld discovered that a metal cooled into the superconducting state in a moderate magnetic field expels the field from its interior. Superconductors are defined as having “a state of perfect diamagnetism.” Perfect diamagnetism implies that the superconducting material does not permit an externally applied magnetic field to penetrate into its interior. Effectively, superconductors block magnetic fields by modifying the magnetic length path, which is known as reluctance.
The exclusion of magnetic flux by a superconductor costs some magnetic energy. As long as this cost is less than the condensation energy gained by going from the normal to the superconducting phase, the superconductor will remain completely superconducting in an applied magnetic field. If the applied field becomes too large, the cost in magnetic energy will outweigh the gain in condensation energy, and the superconductor will become partially or totally normal. The manner in which this occurs depends on the geometry and the material of the superconductor. The geometry that produces the simplest behavior is that of a very long cylinder with the magnetic field applied parallel to its axis. Two distinct types of behavior may then occur, depending on the type of superconductor—Type I or Type II.
Below a critical magnetic field Hc, which increases as the temperature decreases below Tc, the magnetic flux is excluded from a type I superconductor, which is said to be perfectly diamagnetic. For a Type II superconductor, there are two critical magnetic fields, the lower critical magnetic field Hc1 and the upper critical magnetic field Hc2. In applied magnetic fields less than Hc1, the superconductor completely excludes the magnetic field, just as a type I superconductor does below Hc. At magnetic fields just above Hc1, however, flux begins to penetrate the superconductor, not in a uniform way, but as individual, isolated microscopic filaments called fluxoids or vortices, each carrying one quantum of magnetic flux, h/2e. In other words, high levels of static flux are also known to cause vortices in Type II superconductors. The flux penetration is hindered by microscopic inhomogeneities that pin (trap) vortices. As a result, a critical state is formed with some gradient of flux density determined by the critical current.
Vortices provide a means to modulate static flux because they produce a magnetic channel whereby the static flux moves unhindered, without losses from one point to a second point. When a Type II superconductor is placed in a magnetic field B, where Hc1<B<Hc2, and where Hc1 and Hc2 are the lower and upper critical fields, respectively, the magnetic vortices that penetrate the material should form a uniform triangular lattice (Abrikosov vortex lattice), with a lattice spacing determined by the strength of B. If B is increased, the vortices become more closely spaced and their cores start to overlap. At Hc2 the vortex lattice and the Cooper pairing of the electrons disappear and the material becomes normal.
Anisotropy effects are fundamental to superconductivity. Just about all-crystalline superconductors are in principle expected to show some anisotropy effects. There are several classes of materials with anisotropic superconducting properties, including the class of bulk anisotropic superconductors (for example, some of the transition metals) and the class of superconducting thin films. When the thickness of a film is less than the coherence length, the Cooper pairs can only interact with their neighbors in the plane of the film. In this case, the film is commonly referred to as a two-dimensional superconductor, because the Cooper pairs only interact in two directions.
Lowering the effective dimensionality of a superconductor from three to two dimensions has important and measurable consequences, deriving from the fact that the length scale for superconductivity in the direction perpendicular to the film is now the film thickness rather than the coherence length. Usually, layered superconductors show 3D anistropic superconductivity like the bulk transition metals, but sometimes they show 2D superconductivity like thin films, and sometimes they even show entirely new effects.
Research indicates that when a superconductor is irradiated by a laser, the photons get absorbed by the Cooper pairs and this leads to pair breaking. Under certain conditions, a pair breaking avalanche may occur. Previously published research findings show a high quantum pair-breaking efficiency from photons.
It is a well-known fact that permanent magnets produce a static flux that emanates off their end poles. Many devices have been invented that use this static flux to produce electrical power we use today. Static flux is ideal for converting mechanical energy into electrical energy. The basic process has not changed in 100 years. The most common method uses a moving armature that rotates inside windings, making and breaking the magnetic circuit. As Faraday and Maxwell discovered, only then can the static flux be used to extract energy. Faraday's law of induction (Equation 1) states that there is a counter electromotive force generated in a coil of wire when there is a difference in flux over time:
                    ɛ        =                              -            N                    ⁢                                    ⅆ                              Φ                B                                                    ⅆ              t                                                          (                  Eq          .                                          ⁢          1                )            where the magnetic flux ΦB=B A cos θ, and where N is the number of turns of the wire, B is the magnetic field, A is the surface area of the coil, and θ is the angle between B and a line drawn perpendicular to the face of the coil.
The minus sign signifies that the direction of the induced EMF will be such that the magnetic field produced by the induced EMF resists the change in magnetic flux. The presence of the minus sign is referred to as Lenz's Law.
If a device can produce a difference in the flux density passing through a typical coil, then Faraday's law states there would be a counter electromotive force developed across the windings. All of the present day devices that use mechanical energy perform this one simple task. Regardless of the complexity, the device only makes and breaks the flux lines, thereby creating a difference in flux, causing the secondary effect known as counter EMF.